Copolymer dispersant composition for inorganic pigments

ABSTRACT

The present invention is directed to a pigment dispersant composition for use with inorganic pigments in coating compositions. The dispersant composition includes a vinyl or acrylic copolymer and a transition metal or rare earth metal salt. The metal salt in combination with the copolymer is useful with inorganic pigment as it lowers the viscosity of the pigment dispersions, thus allowing a higher concentration of pigment in the dispersion and consequently providing dispersions with higher non-volatile content and higher pigment to binder ratios. The presence of the metal salts in the dispersant composition when used with surface coated metal flake pigment provides excellent corrosion reduction of the metal pigment, indicated by the reduction or elimination of hydrogen gassing by the pigment in a coating composition.

This application is a continuation of Ser. No. 07/982,355, filed Nov.27, 1992, now abandoned.

FIELD OF THE INVENTION

The present invention is directed to a metal salt containing, copolymerpigment dispersant composition for inorganic pigment in aqueous coatingcompositions.

BACKGROUND OF THE INVENTION

Aqueous coating compositions comprise a principal resin, and may containa crosslinker, pigments dispersed in a grind resin and other additivessuch as solvents, control agents, fillers and the like.

Pigments are typically dispersed in a coating composition by means of apigment paste. Pigment pastes are usually prepared by dispersing apigment in a grinding resin in the presence of plasticizers, wettingagents, surfactants or other ingredients in a ball mill, sand mill orcontinuous mill, until the pigment has been reduced to the desiredparticle size and is wetted by the resin or dispersed in it. Suchmethods require lengthy processing times and yield dispersions havingrelatively poor color development and stability, compared tosolvent-based paints.

Dispersing agents for dispersing pigments and dyes in organic liquidsare disclosed in U.S. Pat. No. 4,937,014, to Canestri, issued Jun. 26,1990. This composition contains an amino acid that has first beenreacted with a metal salt and then is reacted with a carboxylic acidterminated polyester.

The present invention is directed to a pigment dispersant compositionfor inorganic pigment usable in an aqueous coating composition. Theinvention provides dispersions containing a salt of a transition metalor rare earth metal. The dispersant compositions are highly effectivefor dispersing inorganic pigment and demonstrate unexpected results bydecreasing the viscosity of the dispersant composition containing theinorganic pigment. As a result of the decreased viscosity a higherconcentration of pigments can be used in the dispersion, resulting in ahiger pigment to binder ratio. Due to increased solids content, thevolatile content of the pigment dispersion is decreased.

When the dispersant composition of the present invention is used withsurface coated metal flake pigments, particularly with aluminum flakepigments, exceptional results are obtained for decreased corrosion ofthe pigment in an aqueous coating composition. This is significantbecause the water-borne coating compositions in use today have a basicpH. The pH of acrylic coating compositions typically ranges from8.0-9.0, and the polyurethane coating compositions typically have a pHranging from 7.5 to 8.0.

Exposure of metal flake pigments to a basic pH aqueous environment,results in the formation of metal hydroxide ions, which are soluble inwater. The production of metal hydroxide ions results in thesolubilization of the metal pigment and the exposure of more pigmentsurface area to the corrosive environment. The formation of metalhydroxide occurs relatively rapidly with metal flake pigments due to thehigh surface to mass ratio of the small particles. The reaction is aform of corrosion and converts the pigment to a hydrated oxide formunsuitable for pigment use, as it destroys the metallic pigmentationproperties of the mirror-like particles. Corrosion is exacerbated sincethe reaction of the metal in water results in the continuous formationof H⁺ ions, evidenced by the production of hydrogen gas, and OH⁻ ions.The H⁺ ions attack and corrode the metal pigment particles and the OH⁻ions cause the pH of the environment to further increase. The high pH ofwater-borne coating systems speeds up the reaction that produces thehydrated metal oxide and results in serious degradation or corrosion ofmetallic flake pigment used in metallic coatings. Contact with theenvironment is continuous over extended periods of time, since coatingscontaining the pigment are often stored for 6 months or more beforeapplication.

It has been found that the transition metal and rare earth metal saltsinhibit corrosion of the metal flake pigment particles, particularlyaluminum flake pigment particles, in the basic pH aqueous coatingenvironment. This is due to a compact film of transition metal or rareearth metal oxides and hydroxides that replace the natural oxide film onthe surface of the metal flake pigment. It is hypothesized that thetransition metal or rare earth metal oxide/hydroxide film forms at localcathodic sites on the surface, where the alkaline conditions generatedby oxygen reduction reactions cause the metal oxide to dissolve and thetransition metal and/or rare earth metal oxide to precipitate.

The present invention is also directed to an aqueous coating compositioncontaining the pigment dispersant compositions and an article coatedwith the coating composition.

SUMMARY OF THE INVENTION

The present invention is a polymeric dispersant composition forinorganic pigments. The dispersant includes a vinyl or acrylic copolymerfunctionalized with isocyanate, anhydride or epoxy functionalities. Thecopolymer may also include polyalkylene glycol homopolymer or copolymerfunctionality, to impart water-miscible character to the polymericbackbone. The copolymer may also include a polar functional compound, tofurther enhance dispersibility of the pigment. The copolymer is admixedwater and with a salt of a transition metal, rare earth metal or mixturethereof to form a dispersant composition.

The copolymer is the reaction product of (i) an ethylenicallyunsaturated monomer having a reactive functionality from which graftingmay take place, where said functionality is an isocyanate functionality,an anhydride functionality or an epoxy functionality; and (ii) at leastone ethylenically unsaturated monomer having no functional group thatreacts with the reactive functionality of monomer (i). The copolymer mayalso include an additional monomer (v) such as an ethylenicallyfunctional aromatic compound.

The copolymer is reacted with a polyalkylene glycol (iii) compound whichis a polyalkylene glycol homopolymer, copolymer, or mixture thereof. Thepolyalkylene glycol reacts with the reactive functionality of monomer(i) to impart water miscible character to the polymer. Usefulpolyalkylene glycol compounds include polyalkylene glycol monoalkylethers and mixtures thereof.

When the reactive functionality of monomer (i) is an isocyanatefunctionality or an anhydride, the polyalkylene glycol compound reactswith the isocyanate or anhydride reactive functionality to form asidechain. When the reactive functionality of monomer (i) is an epoxyfunctionality, the polyalkylene glycol compound must first be reactedwith anhydride to form an acid functional polyalkylene glycol compound.

In one embodiment the copolymer also includes a polar functionalcompound to further enhance dispersibility of the pigment. The polarfunctional compound is selected from the group consisting of alkyl,aryl, and alkylaryl alcohols, acrylic and methacrylic acid,acetoacetate, silane-containing compounds, phosphorus-containingcompounds and urea-containing compounds and mixtures thereof.

The compound with the polar functionality may be incorporated into thedispersant composition through reaction of an ethylenically unsaturatedcompound containing the polar functionality. This can occur by reactionof the polar functional compound with monomer (i) before polymerizationor by copolymerizing one or more ethylenically unsaturated monomerscontaining the polar functionality or functionalities, with theethylenically unsaturated monomers (i) and (ii) or (i), (ii) and (v).

Alternatively, a compound containing a polar functionality may be addedafter the polymerization reaction. This is done by functionalizing thepolymeric backbone to contain isocyanate, hydroxy, epoxy or anhydridefunctionality and then grafting the various polar groups onto thefunctionality. These reactions are explained in greater detail in theDetailed Description.

If any isocyanate functionality provided by monomer (i) remains afterthe polymerization reaction and where applicable, after reacting thepolyalkylene glycol compounds and polar functional compounds, theisocyanate may be capped by the addition of a compound having an amineor hydroxy functionality that reacts with the isocyanate. These amineand hydroxy containing compounds are selected from the group consistingof mono or dialkyl amines, mono or dicycloalkyl amines, aromatic amines,aryl aliphatic amines, mono and di alkanolamines, cyclic alkanolaminesand primary and secondary ether alcohols.

The copolymer is combined with a salt of a transition metal, rare earthmetal or mixtures thereof to form the dispersant composition. Theinorganic pigments are preferably dispersed in an aqueous dispersantcomposition, to form a pigment grind paste. The pigment pastes are mixedwith such ingredients as polymers, crosslinkers, and additional solvents(including additional water) to form an aqueous coating composition.

The addition of the transition metal and/or rare earth metal salt to thecopolymer has a synergistic effect with the copolymer on grindingpigments. Inclusion of the salt results in a significant decrease in theviscosity of the dispersant composition and allows an increase in theconcentration of pigments in the composition. This results in increasedpigment to binder ratio and increased non-volatile content. The saltsare also useful for decreasing the corrosion of metallic flake pigments,particularly chromated aluminum flake pigments, in the aqueous coatingcompositions. Useful salts include metal organic acid salts, halidesalts, and nitrates of the transition metals and rare earth metals andmixtures thereof.

Another aspect of the present invention provides for a compositionhaving a polymeric network containing a residue of the dispersantcomposition described herein above. Such a polymeric network is formedthrough the reactions of species having more than one reactive group,such as polymers and crosslinkers well-known to the art, and thecompound, when the compound contains a group reactive with at least oneof the species, said group forming a covalent bond to become part of thepolymeric network. That part of the polymeric network originallycontained in the compound is termed a residue of the compound. Apolymeric network is formed, for example, during the curing of a coatingcomposition. Preferably, the composition also contains at least oneinorganic pigment that had been dispersed by the compound.

In addition to the effect of the dispersant composion on pigment grindpastes, coating compositions containing surface treated metal flakepigments dispersed in the pigment dispersion compositions of the presentinvention are highly reflective and have excellent appearance. Asdiscussed above, the dispersion compositions reduce or elimatecorrosion, as evidenced by hydrogen gassing in the coatings containingthe metal flake pigments.

Yet another aspect of the present invention provides for a coatedarticle. The coated article is a substrate with a coating thereon. Thecoating on the substrate contains the composition of the invention or apolymeric network containing a residue of the composition, along with atleast one inorganic pigment.

DETAILED DESCRIPTION OF THE INVENTION

The pigment dispersant composition of the present invention includes avinyl or acrylic copolymer having water miscible character and one ormore metal salts of transition metals or rare earth metals.

The copolymer is preferably the reaction product of (i) an ethylenicallyunsaturated monomer having a reactive functionality from which graftingmay take place, where said functionality is an isocyanate functionality,an anhydride functionality or an epoxy functionality; and (ii) at leastone ethylenically unsaturated monomer having no functional group thatreacts with the reactive functionality of monomer (i). The copolymer mayalso include an additional monomer (v) which is an ethylenicallyfunctional aromatic compound.

The ethylenically unsaturated monomer (i) is present in an amountbetween about 5% to about 50% by weight, preferably from about 20% toabout 40% by weight based on total monomer weight. Suitableethylenically unsaturated monomers containing an isocyanatefunctionality include dimethyl-meta-isopropenylbenzyl isocyanate,vinylisocyanate, isocyanatoethyl acrylate and isocyanato ethylmethacrylate, isopropenyl isocyanate, and mixtures thereof. Preferred isdimethyl-meta-isopropenylbenzyl isocyanate, also referred to as TMI®,available from American Cyanamid Co. Wayne, N.J. 076470.

Suitable ethylenically unsaturated monomers containing an anhydridefunctionality include olefinic and cycloolefinic anhydrides andsubstituted olefinic and cycloolefinic anhydrides, provided that thesubstituents do not adversely affect the reactivity of the anhydride orthe properties of the resultant polymer. Examples of these substituentsinclude chloro, alkyl and alkoxy substituents.

Examples of specific anhydrides include dodecenyl succinic anhydride,octadecenylsuccinic anhydride, tetrahydrophthalic anhydride,methyltetrahydrophthalic anhydride, endomethylene tetrahydrophthalicanhydride, chlorendic anhydride, itaconic anhydride, citraconicanhydride, nadic methyl anhydride and maleic anhydride.

Preferred monomers containing the anhydride functionality are itaconicanhydride and maleic anhydride.

Suitable ethylenically unsaturated monomers containing an epoxyfunctionality include glycidyl acrylate, glycidyl methacrylate, andallyl glycidyl ether. The preferred monomer containing the epoxyfunctionality is glycidyl methacrylate.

The ethylenically unsaturated monomers (ii), are present in an amountfrom about 10% to about 90% by weight, preferably from about 40% toabout 70% by weight based on total monomer weight. Suitable monomershaving no functionality that reacts with the reactive functionality ofmonomer (i), include acrylic and methacrylic alkyl, aryl, aryl alkyl andalkoxyalkyl esters. The alkyl esters of acrylic and methacrylic acid arederived from alcohols having from 1 to about 20 carbon atoms, fromphenols or from vinyl monomers.

Preferred are the esters of acrylic and methacrylic acid such as methyl,ethyl, propyl, n-butyl, isobutyl, tert-butyl, cyclohexyl, and2-ethylhexyl acrylates and methacrylates and mixtures thereof.

Also suitable are vinyl chloride, acrylamide and methacrylamide,acrylonitrile, methacrylonitrile, N-alkyl maleimides, N-aryl malemidesand acrolein. Maleic acid and fumaric acid dialkyl esters in which thealkyl groups have 1 to 20 carbon atoms may also be used.

The ethylenically functional aromatic substituted monomer (v), whenincluded, is present in an amount from about 5% to about 40% by weight,preferably from about 10% to about 20% by weight, based on total monomerweight.

Suitable monomers include styrene, alpha-methyl styrene, para-hydroxystyrene, tert-butyl styrene and vinyl toluene and halogenated vinylbenzenes such as chlorostyrene. Also useful are acrylic and methacrylicesters such as para-tolyl acrylate, benzyl acrylate, phenyl ethylacrylate, naphthyl acrylate, benzyl methacrylate, phenyl methacrylate,naphthyl methacrylate, 3-phenylpropyl methacrylate, phenoxyethylmethacrylate. Additional useful monomers are aromatic-containingacrylamides and methacrylamides such as N-phenylacrylamide and mixturesof acrylamides. The preferred ethylenically unsaturated aromaticsubstituted monomers are styrene and phenyl methacrylate.

All weight percentages for the monomers (i), (ii) and (v) reflect avariance of ±5%.

In a preferred embodiment, the copolymer includes a polyalkylene glycolfunctionality to impart water miscible character to the polymer. Thisfunctionality is incorporated by 1) reacting at least one polyalkyleneglycol compound that is a polyalkylene glycol homopolymer, copolymer, ormixture thereof with monomers, before the vinyl or acrylic copolymer isformed or 2) by grafting the polyalkylene glycol homopolymer, copolymer,or mixture thereof on to the copolymer.

The polyalkylene glycol compound is present in an amount between about20% and about 60% by weight, preferably between about 30% and about 40%by weight, based on total non-volatile content of the dispersantcomposition. The weight percentages reflect a variance of ±5%.

Useful compounds for this purpose are polyalkylene glycol monoalkylethers and mixtures thereof. Examples of these include polyalkyleneglycol monoalkyl ethers formed from monoalcohol initiated polymerizationof ethylene oxide, propylene oxide and mixtures thereof with up to 30%by weight propylene oxide. Starting monoalcohols are C₁ -C₁₈ alcoholssuch as methanol, ethanol, n-propanol, iso-propanol, hexanol, decanol,undecanol and ether alcohols such as methoxyethanol, butoxyethanol andthe like. The preferred monoalkyl ethers are polyethylene glycolmonoalkyl ethers, and polyethylene glycol monoalkyl ethers in mixturewith other polyalkylene glycol monoalkyl ethers.

As described above, the polyalkylene glycol compound can be incorporatedinto the polymeric backbone by reaction with monomers, before the vinylor acrylic copolymer is formed. This is accomplished by reacting thepolyalkylene glycol with the reactive functionality on monomer (i) toform a side chain on the monomer before the addition polymerizationreaction between monomers (i), (ii) and (v). When the reactivefunctionality of monomer (i) is an isocyanate or an anhydride, thepolyalkylene glycol compound reacts with the isocyanate or anhydridereactive functionality.

When the polyalkylene glycol is incorporated after the copolymerizationreaction, the polyalkylene glycol reacts with the isocyanate oranhydride functionality on the copolymer to form a sidechain.

With either method of introducing the polyalkylene glycol functionality,when the reactive functionality of monomer (i) is an epoxyfunctionality, the polyalkylene glycol must first be reacted with ananhydride to form an acid functional polyalkylene glycol. The preferredanhydride for this purpose is phthalic anhydride. The acid functionalpolyalkylene glycol can then be reacted with the epoxy functionalmonomer before the polymerization reaction. Alternatively, the acidfunctional polyalkylene glycol can be reacted with the epoxy functionalcopolymer, after the polymerization reaction.

In one embodiment, a compound having a polar functionality is includedin the copolymer to further enhance pigment dispersibility. The polarfunctional group is selected from the group consisting of carboxylicacid, tertiary amine, acetoacetate, silane-containing compounds,phosphorus-containing compounds and urea-containing compounds andmixtures thereof.

Silane-containing compounds can be incorporated into the additionpolymerization reaction in the form of a silane functional ethylenicallyunsaturated monomer. Alternatively, the silane-containing compound canbe incorporated by reacting it with isocyanate, epoxy or anhydridefunctionality on the copolymer backbone.

When reacted with the functionalized copolymer having isocyanate groups,the silane-containing compounds contain isocyanate-reactive groups thatreact with the isocyanate groups on the copolymer. Theisocyanate-reactive groups are selected from hydroxyl, amino, mercapto,or oxirane functional groups. Examples of such materials useful forforming the substituents compatible with the above-mentionedrequirements are 3-aminopropyltrimethoxysilane,3-aminopropyltriethoxysilane, 3-(N-methylamino) propyltrimethoxysilane,3-mercaptopropyltrimethoxysilane, and (3-glycidoxypropyl)methyldiethoxysilane and the like. Preferred are amino-functionalsilanes, especially 3-aminopropyltrimethoxysilane,3-aminopropyltriethoxysilane, and 3-(N-methylamino)propyltrimethoxysilane. The silane functional compounds useful in thepresent invention are disclosed in U.S. Pat. No. 5,156,677 to Carpenteret al. Silane materials that may be utilized in making the compounds ofthe invention are commercially available from, for example, HulsAmerica, Inc., Piscattaway, N.J.; or from Dow Corning Corp., Midland,Mich.; or from Union Carbide Corp., Danbury, Conn.

For reacting with the anhydride functional copolymer, thesilane-containing compounds contain reactive groups that react with theanhydride groups on the copolymer. The anhydride-reactive groups areselected from hydroxyl, primary or secondary amine and mercaptofunctional groups.

For reacting with the epoxy functional copolymer, the silane-containingcompounds contain reactive groups that react with the epoxy groups onthe copolymer. The epoxy-reactive groups include amino, phenol orisocyanate functional groups.

Phosphorus-containing polar functional compounds are incorporated intothe isocyanate functional copolymer by reacting the copolymer with amaterial containing a hydroxyl group and at least one other groupcapable of reacting with isocyanate or latent isocyanate functionalitieson the functionalized copolymer, and subsequently reacting withphosphate containing compounds.

The material containing the hydroxyl group and at least one other groupcapable of reacting with isocyanate or latent isocyanate functionalitiesis a straight or branched compound of one to twelve carbon Atoms. Thegroup capable of reacting with the isocyanate or latent isocyanatefunctionalities may be hydroxyl, amino, or mercapto. Representativeexamples of useful materials are diols, triols, and higher functionalitypolyols, such as ethylene glycol, propylene glycol, butylene glycol,neopentyl glycol, trimethylolethane, trimethylolpropane, 1,6-hexanediol,and pentaerythritol; mercaptoalcohols, such as mercaptoethanol,mercaptopropanol, mercaptobutanol, mercaptophenol, or3-mercapto-1,2-propanediol; and amino alcohols, such as diethanolamine,methylethanolamine, and 6-amino-1-hexanol. Preferably, an amino group orhydroxyl group is chosen to react with the isocyanate. Amino alcoholsare particularly useful.

The amino alcohol is first reacted with the isocyanate functional groupson the functionalized copolymer. The amino group is more reactive toisocyanate than the hydroxyl group. The difference in reactivity isexploited to minimize any crosslinking between functionalizedcopolymers. The reaction between amino and isocyanate groups may beaccomplished under mild conditions, such as by stirring the two togetherfor five minutes at room temperature.

The remaining alcohol group may be converted to the desired phosphatethrough various reaction schemes, such as reaction with polyphosphoricacid, phosphoric acid, phosphorous acid, or phosphorous pentoxide, oranalogs that have phosphorous atoms monosubstituted with an alkyl of oneto ten carbon atoms, an alkoxy of one to ten carbon atoms, an arylalkoxyof two to ten carbon atoms, an alkanoyloxy of two to ten carbon atoms,or a halogen. One preferred method is by addition of polyphosphoric acidat temperatures between about 25° C. and about 200° C. Other well knownmethods, using materials such as phosphorus pentachloride or phosphorusoxychloride, are available.

Phosphorus-containing polar functional compounds are incorporated intothe epoxy functionalized copolymer by reacting the copolymer withpolyphosphoric acid, phosphoric acid, phosphorous acid, or phosphorouspentoxide, or analogs that have phosphorous atoms monosubstituted withan alkyl of one to ten carbon atoms, an alkoxy of one to ten carbonatoms, an arylalkoxy of two to ten carbon atoms, an alkanoyloxy of twoto ten carbon atoms, or a halogen. The phosphorus containing acid oranalog reacts with the epoxy group on the copolymer to form a phosphateester. The phosphate and silane compounds may be utilized separately orin combination.

The urea containing compound may be utilized with other silane orphosphorus-containing compounds or may be utilized alone as the polarfunctional compound. Particularly preferred for purposes of the presentinvention are the urea-containing compounds having the formula: ##STR1##and mixtures thereof, wherein each R is independently selected from thegroup consisting of H, saturated and unsaturated aliphatic and alicycliccompounds that may be substituted or unsubstituted, substituted andunsubstituted aromatic compounds and divalent radicals such as, but notlimited to --NH--, oxygen and sulfur, and wherein one R group has afunctional group which can react with the reactive functionality onmonomer (i). The R group having the reactive functional group isselected from the group consisting of monovalent alkyl radicalssubstituted with hydroxy and amino substituents, and ethylenicallyunsaturated groups substituted with amino, amide, carbonyl, carboxyl,epoxy, hydroxy, ether, ketone, aldehyde and ester functionalities andmixtures thereof. Such urea containing compounds are disclosed in EP 0462 557 A2.

In a preferred embodiment, the R groups of the urea-containing compoundare individually selected from the group consisting of H, alkyl andalkylene, and R'OH where R' is an alkylene group having from 1 to 4carbon atoms and another R is a bond in this alkylene or is anotheralkylene radical. Preferred urea-containing compounds are omega hydroxyalkyl alkylene ureas and omega amino alkyl alkylene ureas. Suchcompounds include aminoethyl ethylene urea and1-(2-hydroxyethyl)-2-imidazolidinone, also known as 2-hydroxyethylethylene urea.

The method for adding the urea-containing compound to the reactionmixture is determined by the functional group of R. If the functionalgroup of R is polymerizable across an ethylenically unsaturated doublebond, the urea-containing compound may be copolymerized with monomers(i) and (ii) or (i), (ii) and (v) as described hereinafter. If thefunctional group on R is not polymerizable, the urea-containing compoundmay be incorporated by grafting onto the functionalized copolymer afterthe polymerization of monomers (i) and (ii) or (i), (ii) and (v). Thegrafting reaction is accomplished by reaction of the urea-containingcompound with the functional group on the copolymer.

In the event that the copolymer is epoxy functional, if the functionalgroup of R is amino it can be reacted directly with the epoxy. If thefunctional group of R is OH, the urea-containing compound must first bereacted with anhydride to form an acid functional urea-containingcompound. As described above, the polyalkylene glycol compound must alsobe acid functional to react with these epoxy functional monomers orpolymers. For grafting the urea-containing compound and the polyalkyleneglycol compound onto an epoxy functional copolymer, the preferred methodof the present invention is to form both the acid functional urea andthe acid functional polyalkylene glycol in one reaction. This isaccomplished by combining the polyalkylene glycol, urea and anhydride,which makes both the polyalkylene glycol and urea acid functional. Thismixture is then combined with the epoxy functional monomer andcopolymerized with monomer (ii), or monomers(ii) and (iii).Alternatively, the epoxy functional copolymer is formed first and theacid functional polyalkylene glycol and urea are grafted on to thecopolymer.

The polar-functional compounds are useful with any of the monomersdefined as monomer (i). The preferred polar functional compounds are thesilane-containing, phosphorus-containing and urea-containing compoundsand mixtures thereof. The polar functional compound(s) is present in anamount between about 1.0 and about 7.0 percent by weight, preferablybetween about 3.0 and about 5.0 percent by weight, based on total nonvolatile content of the dispersant composition. Weight percentages forall polar compounds reflect a variance of ±0.5 percent.

The copolymer is formed by copolymerization using conventionaltechniques such as heating the monomers in the presence of apolymerization initiating agent and optionally chain transfer agents.The copolymerization may be carried out in bulk or solution. For thepresent invention it is preferred to form the copolymer by means of afree radical solution polymerization reaction. Solvents for solutionpolymerization should not have functional groups capable of reactingwith the reactive functionalities on monomer (i).

Suitable solvents include ketones, such as methyl ethyl ketone, methylpropyl ketone and acetone; esters, such as butyl acetate and pentylpropionate; ethers, such as diethylene glycol dimethyl ether, dioxane,tetrahydrofuran; N-methyl pyrrolidone, ketoesters, aromatichydrocarbons, alkanes, cyclic alkanes and mixtures thereof.

Typically initiators are peroxides such as dialkyl peroxides,peroxyesters, peroxydicarbonates, diacyl peroxides, hydroperoxides, andperoxyketals and azo compounds such as2,2'-azobis(2-methylbutanenitrile) and 1,1'-azobis(cyclohexanecarbonitrile).

Typical chain transfer agents are mercaptans such as octyl mercaptan, n-or tert- dodecyl mercaptan; halogenated compounds; thiosalicylic acid,mercaptoacetic acid, mercaptoethanol, buten-1-ol and dimericalpha-methyl styrene. Mercaptans are preferred.

The reaction is usually carried out at temperatures from about 20° C. toabout 200° C. The reaction may conveniently be done at the temperatureat which the solvent or solvent mixture refluxes, although with propercontrol a temperature below the reflux may be maintained. The initiatorshould be chosen to match the temperature at which the reaction iscarried out, so that the half-life of the initiator at that temperatureshould preferably be between one minute and thirty minutes.

The solvent or solvent mixture is generally heated to the reactiontemperature and the monomers and initiator(s) are added at a controlledrate over a period of time, usually between 2 and 6 hours. A chaintransfer agent or additional solvent may also be fed in at a controlledrate during this time. The temperature of the mixture is then maintainedfor a period of time to complete the reaction. Optionally, additionalinitiator may be added to ensure complete conversion.

The NCO number of a copolymer formed from monomer (i) containing anisocyanate reactive functionality and monomer (ii) is from about 0.3meq/g NV to 2.0 meq/g NV, preferably from about 0.9 meq/g NV to about1.4 meq/g NV. The copolymer has a weight average molecular weightdetermined by GPC versus polystyrene standards of from about 3,000 toabout 25,000, preferably from about 4,000 to about 10,000.

As described above, the polyalkylene glycol compound may be added beforeor after the polymerization of monomers (i) and (ii) or (i), (ii) and(v). If the compound is added before the polymerization reaction, it iscombined with monomer (i) and reacts with the reactive functionality onmonomer (i), to form a sidechain. Monomer (i) is then polymerized withmonomers (ii) and, (ii) and (v). This is usually done by an additionpolymerization reaction.

The polyalkylene glycol compound also may be added after thepolymerization of monomers has occurred. In this case the polyalkyleneglycol compound reacts with the reactive functionality on the copolymerto form a sidechain on the copolymer.

If any unreacted isocyanate functionality remains after polymerization,or where applicable after grafting of the polyalkylene glycol and polarfunctional compounds onto the copolymer, the unreacted isocyanate may becapped by the addition of a compound having an amine or hydroxy groupthat reacts with the isocyanate.

The amine or hydroxy containing compound useful for capping theisocyanate is selected from the group consisting of mono or dialkylamines, such as n-propyl amine, isopropyl amine, n-hexyl amine, 2-ethylhexyl amine, n-decyl amine, stearyl amine; C₄ -C₁₈ mono or dicycloalkylamines, such as cyclopentyl amine, cyclohexyl amine, dicyclohexyl amine;heterocyclic C₄ -C₁₈ amines, such as pyrrolidine, piperidine, andmorpholine; aromatic C₆ -C₁₈ amines, such as aniline, p-toluidine,o-toluidine, diphenyl amine, indole and indoline; araliphatic C₇ -C₁₈amines, such as benzyl amine, dibenzylamine and 2-phenyl ethylamine; C₂-C₃₆ mono and di alkanolamines, such as ethanol amine, diethanol amine,isopropanol amine, n-hexanol amine, n-undecanol amine. 3-aminopropanol,aminocyclohexanol, 2-(2-aminoethoxy) ethanol; C₁ -C₃₆ ether alcohols,such as methoxyethanol, butoxyethanol, 1-butoxy-2-propanol,(butoxyethoxy) ethanol and solketal.

The amine or alcohol may be reacted in a stepwise reaction orsimultaneously with the reactive functionality on the copolymer. Thestepwise reaction is preferred. The reaction is usually carried out attemperatures of from about 50° C. to about 130° C. The reaction may becarried out in the presence of the same organic solvents which have beenused in the polymerization reaction and in the presence of a catalystsuch as organic tin compounds and/or tertiary amine.

The final copolymers have a weight average molecular weight of fromabout 3,000 to about 25,000, preferably from about 5,000 to about12,000. The molar ratio of hydrogen functionality on the amino orhydroxy containing compound to the reactive functionality on thecopolymer is from about 0.8 to about 1.3 and preferably from about 1.0to 1.3.

The copolymer is combined with salt selected from the group consistingof the rare earth metal salts, transition metal salts and mixturesthereof, to form a pigment dispersant composition. The transition metaland rare earth metal salts include metal organic acid salts, halidesalts, nitrates, and oxides of the early transition metals having atomicnumbers of 21-28; 39-42; 57 and 72-74; and lanthanide series rare earthmetals having atomic numbers of 58-71; and mixtures thereof. Preferably,the metal salt is selected from the group consisting of acetates ofzirconium, manganese, cerium, yttrium, and lanthanum; nitrates oflanthanum, zirconium and cobalt; and chlorides of lanthanum and hafnium.Examples of these include manganese acetate, cerium acetate, yttriumacetate, lanthanum acetate, lanthanum nitrate, lanthanum chloride,hafnium dichloride oxide, zirconium dinitrate oxide, zirconium nitrate,zirconium acetoacetate, cobalt nitrate and mixtures thereof. The metalsalt is present in an amount between 0.01% and 3.0% by weight, based ontotal dispersant composition weight.

The pigment dispersant composition may be used with inorganic pigments.Examples of these include metal oxides, chromates, phosphates, silicatesand metallic flake pigments. Particular non-limiting examples ofinorganic pigments that could be employed are titanium dioxide, bariumsulfate, ocher, sienna, umber, hematite, limonite, red iron oxide,transparent red iron oxide, black iron oxide, brown iron oxide, chromiumoxide green, zinc oxide, zinc sulfide, zinc chromate, strontiumchromate, barium chromate, zinc phosphate, silicas such as fumed silica,talc, barytes, ultramarine and aluminum flake pigment.

The metal flake pigment that is particularly useful with the presentinvention is chromated aluminum flake pigment. Chromated aluminum is analuminum flake particle surface treated with dichromate salts. Aluminumparticles as contemplated for use with the invention generally have asurface area that may range from about 0.05 to about 15 m² /g ofaluminum. The aluminum particles that are specifically contemplated aspreferred aspects of the invention are chromated aluminum flakes,powders and granules. In a preferred aspect, the surface area of thealuminum is from about 2 to about 14.5 m² /g. The average particle sizeof the aluminum flake pigment is preferably from 1 to 70 microns, morepreferably from 5 to 50 microns.

Commercial chromated aluminum flake pigment pastes are available fromcompanies such as Obron Atlantic Corp., Painesville, Ohio. For certainwaterborne paint applications, such as automotive basecoats, non-leafingaluminum flake pigments, such as 8160 AR aluminum paste from Obron, havebeen utilized.

For the preparation of pigment paste, the pigments or dyestuffs aredispersed in a solution of the copolymer in water with the rare earth ortransition metal salt or a mixture thereof. Optionally, cosolvent,wetting agents, surfactants plasticizers and other ingredients may beincluded. The paste is then ground in a ball mill or other mill. Thepigment paste has a concentration of from about 10 to about 60% byweight of pigments based on the total weight of the pigment paste.

The pigment paste of the present invention is added to water dispersiblefilm forming resin such as those described in Pat. Nos. 4,794,147;4,791,168; 4,518,724; and 4,403,085. These patents also describe theprinciple resin. Preferred principle resins are described in U.S. Pat.Nos. 4,794,147 and 4,791,168.

The concentration of the pigment paste in the aqueous coatingcomposition is from about 10 to about 45% by weight based on the totalweight of the aqueous coating composition.

The addition of a metal salt to the dispersant composition of thepresent invention results in greatly improved dispersibility ofinorganic pigments in pigment grinds. The metal salt allows forincreased pigment concentrations in forming the pigment pastes andgreatly lowers the viscosity of the pigment paste dispersion. Thepigment pastes formed according to the present invention also require avery low level of organic solvents or cosolvents in comparison topigment pastes used heretofore. The combination of increased pigmentconcentration and reduced organic cosolvents in the pigment paste allowfor an unprecedented degree of latitude in formulating a coatingcomposition, especially a coating composition having a lower content ofvolatile organic compounds. Additionally, an increased concentration ofpigment in the pigment paste and reduced milling times improvemanufacturing efficiency and reduce costs associated with themanufacture of the pigment paste dispersion.

Coating compositions of the present invention are formulated by mixingthe pigment dispersions of the present invention, along with othercomponents, into water dispersible basecoat compositions. Examples ofthe water dispersible basecoat compositions include, but are not limitedto, water dispersible film forming resins such as a water dispersiblenon-ionic polyurethane resin of the type disclosed in U.S. Pat. No.4,794,147, a water dispersible anionic polyurethane resin of the typedisclosed in U.S. Pat. No. 4,791,168, or a water dispersible acrylicresin of the type disclosed in U.S. Pat. Nos. 4,403,085 and 4,518,724.

The resin is mixed with an aminoplast resin, polyisocyanate, or othersuitable cross-linking agent, one or more rheology control agents ifdesired, water and a small amount of organic solvent if needed. Otheragents may be included such as various fillers, surfactants,plasticizers, wetting agents, defoamers, adhesion promoters andcatalysts in minor amounts. Other additives may be used, such as organicsolvents, catalysts, conditioning agents, thickeners, rheology controlagents, antioxidants, leveling agents and mixtures thereof.

The basecoat compositions containing the pigment dispersions of thepresent invention are applied to a metal or plastic substrate in one ormore coats. The coating composition may be sprayed or electrostaticallydeposited onto metal or plastic substrates such as, for example,automotive vehicle bodies. Application may be made, for example, by anair atomizer (Binks Model 62 spray gun, available from the Binksmanufacturing Corporation, Franklin Park, Ill.), or by using otherconventional spray methods known in the art.

After being deposited, the basecoat compositions may be flash dried at atemperature sufficient to remove a portion of the solvent, but belowthat sufficient to cure the applied coating, typically temperatureswithin the range of from room temperature to about 145° F. (63° C.).After the first basecoat is deposited, a second basecoat and subsequentlayer of basecoat, if needed or desired can be deposited over the firstlayer, either with or without flash drying. A clear, transparent topcoat layer is then subsequently applied over the last basecoat layer.Any known unpigmented or transparently pigmented coating agent is, inprinciple, suitable for use as the topcoat material.

After the clear coat is applied over the basecoat layer(s), themulti-layer coating is then baked to cross-link and cure the polymericmaterials and to drive the small amount of residual water and/or solventfrom the coating layer(s). This baking step generally involves theheating of the coated substrate for periods of from about 10 to about 60minutes and temperatures ranging between about 150° F. (66° C.) andabout 300° F. (149° C.). The baking step cures the multi-layer coatingto a hard, durable film.

The presence of the rare earth and/or transition metal salt indispersions containing aluminum flake pigments has the effect ofminimizing or eliminating corrosion of the chromated aluminum flakepigments, as evidenced by eliminating or greatly reducing hydrogengassing in the coating composition.

An aluminum flake containing coating composition prepared according tothe present invention applied to an enamel substrate was tested forgassing to determine corrosion resistance of the aluminum flake pigmentin the basic pH environment of the coating. The results are set forth inTable 3.

The coating composition was tested for gassing in the gassing apparatusdescribed above. A 250 ml sample of enamel containing aluminum flakes isfilled into the gas washing bottle. The assembled apparatus containingthe flakes is placed in a 40° C. bath and allowed to equilibrate for 60minutes. After allowing for equilibration, the screw cap is tightenedsecurely. The sample is tested in the 40° C. water bath at 24 hourintervals to measure the amount of hydrogen gas produced. The acceptablemaximum level of generated hydrogen gas is 4 mils after 30 days.

In summary, the dispersant composition of the present inventioncontaining the rare earth and/or transition metal salts provide pigmentdispersions with higher pigment concentration and decreased viscosity.The presence of the rare earth metal salt, transition metal salt ormixture thereof in dispersions containing chromated aluminum flakepigments also minimizes or eliminates corrosion of the pigments, asevidenced by eliminating or greatly reducing hydrogen gassing in thecoating composition. The resultant coatings of the present invention,particularly those containing the chromated aluminum flake pigment, arehighly reflective and demonstrate excellent appearance.

Although certain embodiments of the invention have been selected fordescription in the examples, the examples are merely illustrative and donot in any way limit the scope of the invention as defined in theattached claims.

EXAMPLES Example 1

Preparation of Isocyanate Functional Acrylic Copolymer 1

231.3 g (2.02 mol) of methyl amyl ketone was charged to a reactionvessel fitted with stirrer and condenser. The solvent was heated toreflux temperature and maintained at reflux for the duration of thereaction. A blend consisting of 94.8 g (0.91 mol) styrene, 160.7 g (1.13mol) butyl methacrylate, 144.8 g (1.13 mol) butyl acrylate and 271.7 g(1.35 mol) 1-(1-isocyanato-1-methylethyl)-3-(1-methylethenyl) benzene,hereafter referred to as TMI®, available from American Cyanamid Co.,Wayne, N.J. 07470 , was slowly added over a period of three hours. 67.2g of 50% active tert-butyl peracetate was added to the monomer blend toinitiate the vinyl polymerization. 33.6 g of initiator along with 58.0 gof methyl amyl ketone were added one half hour after the addition ofmonomer was complete. The mixture was heated for an additional 1.5 hoursand then cooled and collected for further modification.

Example 2

Preparation of Epoxy Functional Acrylic Copolymer

222.0 g (1.94 mol) of methyl amyl ketone was charged to a reactionvessel fitted with stirrer and condenser. The solvent was heated toreflux temperature and maintained at reflux for the duration of thereaction. A blend of 104.2 g (1.00 mol) styrene, 210.5 g (1.48 mol)butyl methacrylate, 131.0 g (1.02 mol) butyl acrylate, 72.1 g (0.50 mol)hydroxypropyl methacrylate and 142.2 g (1.00 mol) glycidyl methacrylate,was slowly added over a period of three hours. 66.0 g of 50% activetert-butyl peroxy acetate was added to the monomer blend to initiate thevinyl polymerization. 33.0 g of 50% active initiator along with 55.0 gmethyl amyl ketone were added one half hour after the addition ofmonomer was complete. The mixture was heated for an additional 1.5 hoursand then cooled and collected for further modification.

Example 3

Preparation of Anhydride Functional Acrylic Copolymer

A solvent blend of 110.0 g (0.96 mol) methyl amyl ketone and 20.0 gmethyl propyl ketone was charged to a reaction vessel fitted withstirrer, water trap and condenser. The solvent blend was heated toreflux temperature and maintained at reflux for the duration of thereaction. A monomer blend of 65.4 g (0.63 mol) styrene, 111.6 g (0.78mol) butyl methacrylate, and 100.6 g (0.78 mol) butyl acrylate, wasslowly added over a period of three hours. 40.0 g of 50% activetert-butyl peroxy acetate was added to the monomer blend to initiate thevinyl polymerization. 122.4 g (0.94 mol) itaconic acid was addedsimultaneously with the monomer blend into the reaction vessel at 7.5minute increment shots of solid itaconic acid, followed by washings ofmethyl amyl ketone (47.0 g total). 20.0 g of initiator and 30.0 g ofmethyl amyl ketone were added one half hour after the addition ofmonomer was complete. The mixture was heated for an additional 1.5 hoursuntil 14-16 g of water were removed and then cooled and collected forfurther modification.

Example 4

Preparation of Isocyanate Functional Acrylic Copolymer 2

219.6 g (1.92 mol) methyl amyl ketone was charged to a reaction vesselfitted with stirrer and condenser. The solvent was heated to refluxtemperature and maintained at reflux for the duration of the reaction. Ablend consisting of 248.9 g (1.75 mol) butyl methacrylate, 224.3 g (1.75mol) butyl acrylate, and 301.9 g (1.50 mol) TMI® was slowly added over aperiod of three hours. 77.5 g of 50% active tert-butyl peroxy acetatewas added to the monomer blend to initiate the vinyl polymerization.38.8 g of initiator and 58.4 g of methyl amyl ketone were added one halfhour after the addition of monomer was complete. The mixture was heatedfor an additional 1.5 hours and then cooled and collected for furthermodification.

Example 5

Copolymer Modified With Hydroxyethyl Ethylene Urea (HEEU)-Grind Resin

112.0 g (0.56 mol, average molecular weight of 2000) methoxypolyethylene glycol, 16.5 g (0.13 mol) hydroxyethyl ethylene urea, 4.0 gof a 1% solution of dibutyltin dilaurate in methyl propyl ketone, and300.0 g isocyanate-functional acrylic prepared in accordance withExample 1 were charged to a reaction vessel fitted with a stirrer andcondenser. The mixture was heated to 120° C. and maintained at thattemperature for not more than two hours. At the end of this time, themixture was titrated and the result indicated that all of the methoxypolyethylene glycol and hydroxyethyl ethylene urea had reacted with theisocyanate groups. The remainder of the isocyanate functionality wascapped with 7.5 g (0.12 mol) monoethanolamine which was added over aperiod of 5-10 minutes while the mixture was stirred and the temperaturewas approximately 90° C. The temperature then rose to 100° C. and thensubsided. When the exothermic reaction had ceased, the mixture wastitrated. Titration revealed no remaining isocyanate functionality. Thematerial was subsequently dispersed with 10.0 g (0.55 mol) of deionizedwater.

Example 6

Copolymer Modified With Phosphate Ester-Grind Resin

96 g (0.47 mol, average molecular weight of 2000) methoxy polyethyleneglycol, 3.7 g of a 1% solution of dibutyltin dilaurate in methyl propylketone, and 300.0 g isocyanate-functional acrylic prepared in accordancewith Example 1 were charged to a reaction vessel fitted with a stirrerand condenser. The mixture was heated to reflux and maintained at refluxfor not more than one hour. At the end of this time, the mixture wastitrated and the result indicated that all of the methoxy polyethyleneglycol had reacted with the isocyanate groups.

After the mixture had cooled to approximately 60° C., 17.9 g (0.29 mol)ethanolamine was added. The temperature then rose to 90° C. and thensubsided. The mixture was titrated and the result indicated no remainingisocyanate functionality.

Next, polyphosphoric acid 19.9 g, (0.08 mol.) was added along with 100 gtoluene. The mixture was heated to reflux 25° C., for approximatelythree hours.

Example 7

Titanium Dioxide Pigment Paste With Phosphate Modified Copolymer andCerium Triacetate

To a stirred mixture of phosphate modified copolymer 73.8 g, prepared byEx. 6, propylene glycol monomethyl ether 80 g, and N-methylpyrrolidone10 g was added deionized water 1123 g, and the resultant mixture wasstirred for approximately ten minutes. Next, titanium dioxide¹ 1200 g,was added slowly, over 1-2 minutes, to the above solution and stirredwith a Cowles blade for approximately 15 minutes. Cerium triacetate 9.6g was then added to the above mixture, whereupon a noticeable drop inviscosity occurred within seconds of the addition of the cerium salt.The resultant mixture was then ground on a gravity sand mill until thelargest pigment particle observable was less than 4 microns.

¹ Titanium dioxide sold under trademark Tipure, from DuPont de Nemours,E. I. Co., Wilmington, Del.

Example 7A

Titanium Dioxide Pigment Paste With Phosphate Modified Copolymer(Control)

A titanium dioxide pigment paste was prepared according to Example 7,without the Cerium triacetate.

Example 8

Iron Oxide Pigment Paste

To a stirred mixture of 19.7 grams phosphate modified copolymer,prepared by Ex. 6, 3.0 grams propylene glycol mono methyl ether and 3.0grams N-methylpyrrolidone was added 242.0 grams deionized water withstirring (via Cowles blade), and stirred for 5-15 minutes. Iron oxidepigment¹, 154 g, was added slowly, over 1-2 minutes, to the abovesolution and stirred with a Cowles blade for approximately 15 minutes.1.1 gram Cerium triacetate was then added to the above mixture,whereupon a noticeable drop in viscosity occurred within seconds ofaddition of the cerium salt.

The resultant mixture (pre-mix) was then ground on a miniature attritorusing steel shot media until the largest pigment particle sizeobservable was less than 4 microns. The ground paste was then filteredto remove the steel shot media affording the pigment paste.

It should be noted that the viscosity reduction caused by the ceriumsalt is independent of the addition order of the cerium salt. Forexample, the viscosity reduction occurred when the cerium salt was addedto the pre-mix, during the grinding or milling process, or after themilling process. In all cases viscosity reduction occurs.

¹ Iron oxide used was Ferric oxide from BASF Corp.

Example 8A

Iron Oxide Pigment Paste 2 (Control)

A pigment paste was prepared as described in Example 8, without theCerium triacetate.

Example 9

Titanium Dioxide Pigment Paste with HEEU Modified Copolymer and CeriumTriacetate

To a stirred mixture of 62.0 grams dispersant containing HEEU preparedaccording to Ex.5, 45.0 grams propylene glycol mono methyl ether and45.0 grams propylene glycol mono butyl ether was added 1123.0 gramsdeionized water, with stirring (via Cowles blade), and stirred for 5-15minutes. The titanium dioxide pigment¹, 1200.0 grams, was added slowly,over 1-2 minutes, to the above solution and stirred with a Cowles bladefor approximately 15 minutes. 0.12 gram Cerium triacetate was then addedto the above mixture, whereupon a noticeable drop in viscosity occurredwithin seconds of addition of the cerium salt. The resulting paste wasground in a sand mill for three passes.

¹ Titanium dioxide pigment sold under trademark Tipure, from DuPont deNemours, E. I. Co., Wilmington, Del.

Example 9A

Titanium Dioxide Pigment Paste (Control)

A titanium dioxide containing pigment paste was prepared according toexample 9, but without the addition of Cerium triacetate.

Example 10

Fumed Silica Paste

A fumed silica paste was prepared by mixing together 12.16 parts byweight Aerosil® R-972 fumed silica (Degussa Corporation, 2 Penn PlazaNew York, N.Y.), 31.36 parts by weight isopropanol, 17.10 parts byweight monobutyl ethylene glycol ether, and 5.90 parts by weightResimene®, 747 methylated melamine formaldehyde resin, available fromMonsanto Corp. 800 N. Lindbergh Blvd., St. Louis Mo. 63167. Theresultant mixture was stirred on cowles for approximately thirty minutesafter which 33.48 parts by weight nonionic polyurethane grind resin wasadded. The mixture was then run through a sand mill for two passes.

The nonionic polyurethane resin was prepared according to the teachingsof U.S. Pat. No. 4,794,147, the contents of which are incorporatedherein by reference.

Example 11

Carbon Black Tint

The carbon black tint was prepared by mixing together 5.51 partsdeionized water and 10.49 parts black pigment Monarch 900, availablefrom Cabot Corp. Billerica, Mass. 01821. This mixture was added to 84.00parts nonionic polyurethane resin with rapid stirring.

The resultant mixture (pre-mix) was then ground on an attritor usingsteel shot media until the largest pigment particle size observable wasless than 4 microns. The ground paste was then filtered to remove thesteel shot media affording the pigment paste.

The nonionic polyurethane resin was prepared according to the teachingsof U.S. Pat. No. 4,794,147, the contents of which are incorporatedherein by reference.

Coating Composition I

With Cerium Acetate Treated Titanium Dioxide

    ______________________________________                                        Ingredient             Parts by weight                                        ______________________________________                                        1. Pluricol P-1010.sup.1 and 3% Laponite.sup.2                                                       13.61                                                  dispersion in water                                                           2. Resimene ® 747 methylated melamine.sup.3                                                      6.87                                                   3. Ethylene glycol monobutyl ether                                                                   1.72                                                   4. Nonionic polyurethane resin                                                                       27.87                                                  dispersion.sup.4                                                              5. Fumed Silica dispersion (Example 10)                                                              7.97                                                   6. Titanium dioxide (white) pigment                                                                  39.67                                                  paste (Example 9)                                                             7. Carbon black tint (Example 11)                                                                    0.12                                                   8. Nacure ® 2500 blocked acid catalyst.sup.5                                                     1.88                                                   9. Tinuvin 1130.sup.6  0.29                                                   ______________________________________                                         .sup.1 Surfactant from BASF Corporation, Wyandotte, MI 48192.                 .sup.2 Synthetic bentonite clay from Laporte, Incorporated, Saddle Brook,     NJ 07662.                                                                     .sup.3 Melamine crosslinker from Monsanto Corporation, St. Louis, MO          63167.                                                                        .sup.4 The nonionic polyurethane resin was prepared in accordance with th     teachings of U.S. Pat. No. 4,794,147.                                         .sup.5 Blocked acid catalyst from King Industries, Norwalk, CT 06852.         .sup.6 UV absorber from CibaGeigy Corp. Additives Division, Hawthorne, NY     10532.                                                                   

Components 2 and 3 were premixed, then added to component 1 with rapidstirring. To this mixture were then added, successively with rapidstirring, components 4-9. After mixing of all components, stirring wascontinued for about one hour, after which the coating was filtered intoa container and capped for later use.

Coating Composition II

With Cerium Triacetate Treated Cromated Aluminum Flake Pigment and HEEUPolar Functional Compound

A slurry was prepared from the following ingredients.

    ______________________________________                                        1. Cymel ® 327.sup.1  20.6   g                                            2. 2-ethyl hexanol        17.0   g                                            3. Dispersant resin containing                                                                          13.2   g                                            2-hydroxyethyl ethylene urea (HEEU)                                           based dispersant grind resin (Ex. 5)                                          4. Cerium triacetate      0.2    g                                            5. Chromated aluminum flake pigment.sup.2                                                               29.2   g                                            6. Deionized water        10.0   g                                            ______________________________________                                    

First a mixture of the Cymel® 327 and 2-ethyl hexanol was prepared. Nextthe HEEU based dispersant grind resin was added to the mixture. In aseparate vessel the cerium triacetate and water were combined withmixing and then added to the first mixture. The aluminum pigment wasthen added. The mixture was then agitated for 15 minutes.

Next the following ingredients were added as described below.

    ______________________________________                                        Emulsion resin.sup.3     181.5  g                                             Dimethylethanolamine 5% (DMEA)                                                                         10.6   g                                             Viscalex ® HV-30.sup.4                                                                             6.7    g                                             Deionized water          74.4   g                                             Propylene glycol propyl ether                                                                          72.0   g                                             ______________________________________                                    

First the resin and 5% DMEA were combined to provide a resin with a pHof 8. In a separate container the Viscalex® and water were combined andthen added slowly to the resin. Next, the propyl ether was added to themixture. Finally, the aluminum slurry was added to the mixture, withmixing for 5-10 minutes. The coating was then neutralized to a pH of 8with additional 19.3 g of 5% DMEA. After 2 days the paint was reduced tospray viscosity with the addition of 138.1 g deionized water to achievea viscosity of 96.8 cP on a Bohlin V-88 viscometer.

¹ A methylated melamine formaldehyde resin, sold under the trademarkCymel® and available from American Cyanamid Co.

² Chromated aluminum pigment from Obron Atlantic Corp., Painesville,Ohio.

³ Acrylic uncrosslinked core-shell polymeric emulsion resin having 45%non-volatile content.

⁴ Rheology control agent sold under the trademark Viscalex® andavailable from Allied Colloids Inc., Suffolk, Va.

Coating Composition IIa

A coating composition was prepared as in Coating II, except that thefinal pH was adjusted to 8.5 instead of 8.0.

Coating Composition IIb

A coating composition was prepared as in Coating II, except thatpropylene glycol propyl ether was substituted for the 2-ethyl hexanol inthe slurry formulation.

Coating Composition III

With Cerium Triacetate Treated Chromated Aluminum and Phosphate PolarFunctional Compound

A slurry was prepared from the following ingredients.

    ______________________________________                                        1. Cymel ® 327.sup.1  25.80  g                                            2. 2-ethyl hexanol        21.30  g                                            3. Phosphate Ester based dispersant                                                                     19.30  g                                            Grind Resin (Ex. 6)                                                           4. Cerium triacetate      0.25   g                                            5. Chromated aluminum flake pigment.sup.2                                                               36.50  g                                            6. Deionized water        15.00  g                                            ______________________________________                                    

First a mixture of the Cymel® 327 and 2-ethyl hexanol was prepared. Nextthe phosphate ester compound was added to the mixture. In a separatevessel the cerium triacetate and water were combined with mixing andthen added to the first mixture. The aluminum pigment was then added.The mixture was agitated for 15 minutes.

Next the following ingredients were added as described below.

    ______________________________________                                        Emulsion resin.sup.3     226.4  g                                             Dimethylethanolamine 5% (DMEA)                                                                         13.4   g                                             Viscalex ® HV-30.sup.4                                                                             8.4    g                                             Deionized water          92.5   g                                             Propylene glycol propyl ether                                                                          90.0   g                                             ______________________________________                                    

First the resin and 5% DMEA were combined to provide a resin with a pHof 8. In a separate container the Viscalex® and water were combined andthen added slowly to the resin. Next, the propyl ether was added to themixture. Finally, the aluminum slurry was added to the mixture, withmixing for 5-10 minutes. The coating was then neutralized to a pH of 8with an additional 37.2 g of 5% DMEA. After 2 days the paint was reducedto spray viscosity with the addition of 188.1 g deionized water toachieve a viscosity of 85.3 cP on a Bohlin V-88 viscometer.

¹ A methylated melamine formaldehyde resin, sold under the trademarkCymel® and available from American Cyanamid Co.

² Chromated aluminum pigment from Obron Atlantic Corp., Painesville,Ohio.

³ Acrylic uncrosslinked core-shell polymeric emulsion resin having 45%non-volatile content.

⁴ Rheology control agent sold under the trademark Viscalex® andavailable from American Colliods Inc., Suffolk, Va.

                                      TABLE 1                                     __________________________________________________________________________    COMPARATIVE SAMPLES OF PIGMENT DISPERSANT COMPOSITIONS                        Pigment dispersant compositions were prepared according to the methods        set forth in                                                                  examples 7-9 and having the parameters as set forth in Table 1 for polar      functional                                                                    compound and % metal salt. The pigment to binder ratios, % non-volatile       content and %                                                                 pigment are set forth in Table 1 for comparison of compositions with and      without metal salts.                                                                                  PIGMENT                                                        POLAR          TO    % NON-                                                   FUNCTIONAL                                                                             % METAL                                                                             BINDER                                                                              VOLATILE                                                                             %                                        EX PIGMENT                                                                             COMPOUND SALT* RATIO CONTENT*                                                                             PIGMENT*                                 __________________________________________________________________________    A  Titanium                                                                            phosphate                                                                              1.3%  45    61.4   58.5                                        Dioxide        Cerium                                                                        Triacetate                                                  B  Titanium                                                                            phosphate                                                                              --    25    50.18  48.25                                       Dioxide                                                                    C  Iron Oxide                                                                          phosphate                                                                              .26%  15    39.7   36.4                                                       Cerium                                                                        Triacetate                                                  D  Iron Oxide                                                                          --       --    8     32.6   30.1                                     E  Titanium                                                                            HEEU.sup.a                                                                             1.3%  35    61.5   58.66                                       Dioxide        Cerium                                                                        Triacetate                                                  F  Titanium                                                                            HEEU.sup.a                                                                             --    15.75 46.9   44.1                                        Dioxide                                                                    __________________________________________________________________________     *All percentages are based on total dispersant composition weight.            .sup.a Dispersant with HEEU is hydroxy ethyl ethylene urea.              

As can be seen from Table 1, pigment to binder ratio increased, thepercentage of pigment in the dispersant composition increased and thenonvolatile content of the dispersant composition increased with theintroduction of the metal salt to the dispersant composition.

                                      TABLE 2                                     __________________________________________________________________________    COMPARISON OF EFFECT ON VISCOSITY OF DISPERSANT COMPOSITIONS                  WITH AND WITHOUT TRANSITION METAL OR RARE EARTH METAL SALTS                   Pigment dispersions containing titanium dioxide and phosphate dispersant      were prepared fol-                                                            lowing the method of Example 7. A dispersant composition containing           cerium acetate, label-                                                        led Ex. A, and a control without cerium acetate, labeled Ex. B, were          compared to determine                                                         the effect of the metal salt on viscosity. The results are set forth in       the following table.                                                                        PIGMENT      % NON-                                                      METAL                                                                              TO BINDER                                                                            PERCENT                                                                             VOLATILE                                           EX PIGMENT                                                                             SALT RATIO  PIGMENT                                                                             CONTENT                                                                              VISCOSITY.sup.a                             __________________________________________________________________________    A  Titanium                                                                            0.38 25     43.1  50.4   45 KU @ 23° C.                          Dioxide                                                                    B  Titanium                                                                            --   25     48.1  50.18  59 KU @ 23° C.                          Dioxide                                                                    __________________________________________________________________________     .sup.a Viscosity was measured with a Stormer viscometer, Ser. No. 86031,      manufactured by Thomas Scientific.                                       

As can be seen from Table 2, the addition of the cerium acetate metalsalt lowers the viscosity of the dispersant composition.

                                      TABLE 3                                     __________________________________________________________________________    GASSING RESULTS FOR CHROMATED ALUMINUM FLAKE CONTAINING                       COATINGS TREATED WITH DISPERSANT COMPOSITION                                  Gassing results for coating compositions containing chromated aluminum        flake pigment in com-                                                         bination with the dispersant compositions containing transition metal or      rare earth metal salts                                                        are set forth in the following table.                                                       SOLVENT FINAL                                                                              GASSING RESULTS IN ML                              COATING                                                                             POLAR CPD                                                                             FOR SLURRY                                                                            pH   14 DAYS                                                                             21 DAYS                                                                             30 DAYS                                __________________________________________________________________________    II    HEEU.sup.a                                                                            EH.sup.c                                                                              8.0  0     0     0                                      IIa   HEEU.sup.a                                                                            EH.sup.c                                                                              8.5  2     3     3                                      IIb   HEEU.sup.a                                                                            PG.sup.d                                                                              8.0  2     2     2                                      III   PHOSPHATE.sup.b                                                                       EH.sup.c                                                                              8.0  2     2     2                                      __________________________________________________________________________     .sup.a Heeu is hydroxy ethyl ethylene urea compound of Ex.                    .sup.b Phosphate is the phosphate ester compound of Ex. 6.                    .sup.c EH is ethyl hexanol                                                    .sup.d PG is propylene glycol                                            

We claim:
 1. A pigment dispersion comprising inorganic pigment and apolymeric pigment dispersent comprising the reaction product of(i) anethylenically unsaturated monomer having a reactive functionality whichis selected from the group consisting of isocyanates, anhydrides, andepoxy functionalities, (ii) at least one ethylenically unsaturatedmonomer having no reactive functionality to react with the reactivefunctionality of monomer (i), (iii) a polyalkylene glycol compoundselected from the group consisting of polyalkylene glycol monoalkylethers and mixtures thereof, and (iv) a compound having polarfunctionality selected from the group consisting of silane-containingcompounds having hydroxyl, amino, mercapto, isocyanato or oxiranefunctional groups; phosphorus containing compounds having hydroxyl,amino, or mercapto functionalities; and urea-containing compounds havingthe formula ##STR2## wherein each R is independently selected from thegroup consisting of H, alkyl, alkylene, and R'OH where R' is an alkylenegroup having from 1 to 4 carbon atoms, and the reaction product of(i)-(iv) is reacted with a metal salt selected from the group consistingof transition metal and rare earth metal salts, wherein the metal saltis present to enhance pigment concentration in the dispersion, in anamount between 0.01 and 3.0 percent based on total weight of thepolymeric pigment dispersent and metal salt.
 2. The pigment dispersionof claim 1, wherein the transition metal and rare earth metal salt isselected from the group consisting of metal organic acid salts, halidesalts, nitrates, oxides of the transition metals and rare earth metalsand mixtures thereof.
 3. The pigment dispersion of claim 1, wherein thetransition metal and rare earth metal salt is selected from the groupconsisting of acetates of zirconium, manganese, cerium, yttrium, andlanthanum; nitrates of lanthanum, zirconium and cobalt; and chlorides oflanthanum and hafnium.
 4. The pigment dispersion of claim 1, wherein thetransition metal and rare earth metal salt is selected from the groupconsisting of manganese acetate, cerium acetate, yttrium acetate,lanthanum acetate, lanthanum nitrate, lanthanum chloride, hafniumdichloride oxide, zirconium dinitrate oxide, zirconium nitrate,zirconium acetoacetate, iron chloride, cobalt nitrate, and mixturesthereof.
 5. The pigment dispersion of claim 1, wherein the ethylenicallyunsaturated monomer having a reactive functionality (i) is selected fromthe group consisting of1-(1-isocyanato-1-methylethyl)-3-(1-methylethenyl)benzene, isocyanatoethylacrylate, isocyanato ethyl methacrylate, itaconic anhydride, maleicanhydride, and glycidyl methacrylate.
 6. The pigment dispersion of claim1, wherein the ethylenically unsaturated monomer (ii) is selected fromthe group consisting of acrylic and methacrylic alkyl, aryl, aryl alkyl,alkoxyalkyl and aryloxyalkyl esters derived from alcohols having from 1to 20 carbon atoms and mixtures thereof.
 7. The dispersant compositionof claim 1, wherein the ethylenically unsaturated monomer (ii) isselected from the group consisting of methyl, ethyl, propyl, n-butyl,isobutyl, tert-butyl, cyclohexyl, 2-ethylhexyl, acrylates andmethacrylates.
 8. The dispersant composition of claim 1, wherein thecompound having polar functionality is present in an amount between 1.0and 7.0 percent by weight based on total non-volatile content of thedispersant composition.
 9. The dispersant composition of claim 1,wherein the urea-containing compound includes R having a functionalityreactive with monomer (i), includes an R functionality selected from thegroup consisting of R'OH and R'NH₂ where R' has a carbon chain length offrom 1 to 8 carbon atoms.
 10. The dispersant composition of claim 1,wherein the pigment dispersent includes unreacted isocyanate and thepigment dispersent further comprises a compound for capping anyunreacted isocyanate functionality remaining after the polymerizationreaction of monomers (i) and (ii), wherein said compound is selectedfrom the group consisting of mono amines, dialkyl amines, monocycloalkylamines, dicycloalkyl amines, heterocyclic amines, aromatic amines,araliphatic amines, monoalkanolamines, di- alkanolamines and etheralcohols.
 11. The dispersent composition of claim 1 wherein the pigmentis a chromated aluminum flake pigment.
 12. The dispersant composition ofclaim 1, wherein the urea containing compound is 2-hydroxyethylethyleneurea, having the formula ##STR3##
 13. The dispersant composition ofclaim 1, wherein the polymeric pigment dispersion is polymerized from(i)ethylenically unsaturated monomer having a reactive functionality,selected from the group consisting of1-(1-isocyanato-1-methylethyl)-3-(1-methylethenyl)benzene, isocyanatoethylacrylate, isocyanato ethyl methacrylate, itaconic anhydride, maleicanhydride, glycidyl methacrylate, and mixtures thereof, and (ii) atleast one ethylenically unsaturated monomer selected from the groupconsisting of acrylic and methacrylic alkyl, aryl, aryl alkyl,alkoxyalkyl, aryloxyalkyl esters, and mixtures thereof.
 14. Thedispersant composition of claim 13, further comprising ethylenicallyfunctional aromatic compound (v), selected from the group consisting ofstyrene, alpha-methyl styrene, tert-butyl styrene, para-hydroxy styrene,vinyl toluene, naphthyl acrylate, phenyl ethyl acrylate, phenylmethacrylate, naphthyl methacrylate, 3-phenylpropyl methacrylate,phenoxyethyl methacrylate, halogenated vinyl benzenes and mixturesthereof.
 15. The pigment dispersion of claim 1, further comprisingwater.
 16. The dispersant composition of claim 15, wherein the polymericpigment dispersion is the reaction product of monomers (i) and (ii) andfurther comprises (v) an ethylenically-unsaturated aromatic monomer. 17.The dispersant composition of claim 16, wherein the ethylenicallyfunctional aromatic compound (v) is selected from the group consistingof styrene, alpha-methyl styrene, tert-butyl styrene, para-hydroxystyrene, vinyl toluene, naphthyl acrylate, phenyl ethyl acrylate, phenylmethacrylate, naphthyl methacrylate, 3-phenylpropyl methacrylate,phenoxyethyl methacrylate, halogenated vinyl benzenes and mixturesthereof.